Some studies of an unusual eucrite: Ibitira |
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| Authors: | Laurel L Wilkening Edward Anders |
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| Institution: | Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, U.S.A.;Enrico Fermi Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, U.S.A. |
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| Abstract: | The Ibitira eucrite is remarkable both for its vesicles and its unbrecciated nature. It consists of ~63 vol. % pyroxene (Wo14En38Fs48), 31% plagioclase (An95–96), ~2% of nickel-iron, troilite, ilmenite, titanian chromite, and 4% of a silica polymorph. It has a mean track density of 1.8 ± 0.3 × 106 cm?2, mainly due to cosmic rays. Its pre-atmospheric radius must have been at least 10 cm.The absence of complex radiation effects and presence of vesicles place constraints on the thickness of the Ibitira basalt flow. From the freezing time calculations of Provost and Bottinga, it appears that Ibitira came from a flow no less than 2.5 m and probably no more than 10 or 20 m thick. However, this estimate depends strongly on the viscosity of the melt, which is not well known. |
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